This proposal is based on the hypothesis that oxidative stress and injury is a common and major driving force of hepatocellular carcinoma (HCC) in chronic liver diseases and that decreased antioxidant capacity increases the probability of HCC development in patients with chronic liver diseases. Therefore, the long term objectives of this proposal are to determine the mechanism underling oxidative stress-mediated HCC development from hepatitis C (HCV) infection and to identify risk factors and oxidative stress-mediated biomarkers associated with the progression of HCC. Several clinical studies showed a causal relationship between low levels of superoxide dismutase (SOD) and the development of HCC;several mouse models generated to recapitulate HCC development were shown to have elevated levels of oxidative damage;and mutant mice with genetic defects in oxygen free radical metabolism develop HCC after a long incubation time. Collectively, these studies suggest that oxidative stress may play a direct and important role in the development of HCC in chronic liver diseases. We will focus our studies on the interplay between HCV-mediated HCC development, oxidative stress, and SOD deficiency in this proposal. Three Specific Aims are proposed to determine the relationship between HCV infection, ROS production, calcium homeostasis, and hepatocarcinogenesis, to determine the role of SOD in the development of HCV-mediated hepatocarcinogenesis, and to identify molecular targets common to chronic HCV infection and SOD deficiency by comparative proteomic analyses. In vitro and in vivo studies using established human liver cell line, primary human hepatocytes, HCV transgenic mice, and CuZnSOD deficient mice will be carried out to determine the effects of HCV proteins on ROS production, calcium homeostasis, and the activation of redox-sensitive signaling molecules. A genetic approach will be used to reduce SOD levels in HCV transgenic mice to modulate the course of HCC development. In addition, different proteomic tools and procedures will be implemented to identify molecules that are vulnerable to oxidative modification in HCV transgenic and CuZnSOD deficient mice.